| 1. |
- Arnell, Matilda, 1987-
(author)
-
Distribution patterns of fleshy-fruited woody plants at local and regional scales
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- Fleshy-fruited woody plants share a long history with humans, providing us with food and wood material. Because of this relation, we have actively moved some of these plants across landscapes and continents. In Sweden, these species are often found in open and semi-open habitats such as forest edges, their fruits are most often dispersed by birds and their flowers are, with some exceptions, pollinated by insects. In this thesis my overall aim was to map and analyse distribution patterns of fleshy-fruited woody plants in Sweden to expand our knowledge on the mechanisms governing their distributions. First, I mapped a population of the early flowering, fleshy-fruited shrub Daphne mezereum (common mezeron, tibast) and surveyed the reproduction and fruit removal of all individuals (chapter I). My main aim was to investigate to what extent reproduction and fruit removal was affected by local distribution patterns. Secondly, I mapped local distribution patterns of fleshy-fruited woody species and analysed spatial associations between life stages and species (chapter II). My main aim was to relate these spatial associations to predictions of how bird dispersal would shape the local distribution patterns and the hypothesis that birds create ‘wild orchards’. Thirdly, I digitized historical maps and surveyed fleshy-fruited woody species along transects across landscapes (chapter III). My aim was to examine the hypothesis that these species accumulate in open and semi open habitats created by human land use. Fourthly, I estimated range filling of woody plants in Sweden at a 1 km2 resolution (chapter IV). My aim was to compare these estimates among species with different dispersal systems to understand the effect of dispersal on the occupancy of woody species at regional scales.I found the distribution patterns of these species to be affected by past and present land use, supporting the hypothesis that these plants accumulate in open habitats. Occurrences of species in this guild in todays’ forest are positively related to past human land use (chapter III) and the density of D. mezereum increases with decreasing distances to forest edges (chapter I). This accumulation may in part be explained by the positive effect of forest edges on reproduction and fruit removal (chapter I). I further found local distribution patterns of this guild and the individual species to be aggregated (chapter I and II), and spatial associations between saplings and reproductive individuals to support the ‘orchard’ hypothesis (chapter II). The aggregated pattern of fruit-bearing individuals was positively related to fruit removal whereas aggregated flowering individuals was negatively related to fruit set (chapter I). On the regional scale, I found these species to occupy climatically suitable areas, or fill their potential ranges, to a less extent that wind dispersed trees and shrubs (chapter IV), which may indicate dispersal limitation.In conclusion, the behaviour of birds and humans have shaped, and still shape the current distribution of fleshy-fruited trees and shrubs in Sweden, resulting in accumulation in open habitats and locally aggregated distribution patterns. Changing land-use practices and potential mismatches between fruit maturation and bird dispersal with a changing climate may thus result in even lower chances of these species to fill their potential ranges, due to habitat losses and dispersal limitations at local and regional scales.
|
|
| 2. |
- Marteinsdóttir, Bryndís, 1980-
(author)
-
Plant community assembly in grazed grasslands
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- Species assembly into local communities from the surrounding region can be caused either by species failure to reach the site (i.e. seed limitation) or to establish (i.e. establishment limitation). The aim of this thesis was to investigate plant species assembly and to determine the relative importance of different factors in that process.In a cultivated landscape in southeast Sweden, plant community assembly was studied in grazed ex-arable fields. Community assembly from the surrounding region into the local community was explored using trait-based null models and seed sowing and transplanting experiments. The influence of local environmental factors and landscape history and structure on community assembly was also studied. In addition, differences in species assembly between ex-arable fields and semi-natural grasslands were explored.Seed limitation was the strongest filter on local community assembly. Only a fraction (36%) of species in a region dispersed to a local site and adding seeds/transplants increased species establishment. Species abundance at the regional scale, species dispersal method and seed mass strongly influenced which species arrived at the local sites. Establishment limitation also affected the assembly. Of species arriving at a site 78% did establish, seedling survival was low and which species established was influenced by species interactions, local environmental conditions and stochastic events. In addition, landscape structure that determined the species richness in the regional species pool influenced the local assembly. The comparison between assembly in ex-arable fields and semi-natural grasslands indicated that the main cause of difference in species assembly between them was difference in their age.The main conclusion of this thesis is that regional processes are more important than local factors in determining plant community assembly.
|
|
| 3. |
- Jakobsson, Simon, 1987-
(author)
-
Wooded or treeless pastures? : Linking policy, farmers' decisions and biodiversity
- 2018
-
Doctoral thesis (other academic/artistic)abstract
- Worldwide, biodiversity conservation is one of the key challenges for a sustainable future of nature and society. It is particularly important to preserve high quality habitats within otherwise intensively managed agricultural landscapes. Within the European Union (EU), farmers are highly dependent on agricultural subsidies through the Common Agricultural Policy (CAP), which hence have a strong influence on management and biodiversity. In European agricultural landscapes, wooded pastures form important habitats that contribute to landscape level heterogeneity and high local biodiversity, values which are often closely linked to trees. Unfortunately, many of these values were put at risk when a tree density limitation was introduced within the CAP, encouraging farmers to keep pastures open and ensuring grazing management. However, limiting tree density to a specific number to increase biodiversity finds little basis in the scientific literature. The main objective of this thesis is therefore to investigate how different measures of biodiversity across multiple taxa are affected by tree density and to study the farmers' perspective on this CAP regulation. Wooded pastures in the biosphere reserve Östra Vätterbranterna in southern Sweden were used as study sites. This thesis shows that encouraging farmers to cut trees to receive subsidies weakens the link between social and ecological values of wooded pastures, with potential subsequent losses in biodiversity. Trees were almost exclusively positive for biodiversity within this study system, increasing the species richness of plants, birds and bats. However, functional diversity across these taxa were mainly affected by other vegetation attributes within and around the pastures, such as shrub density and surrounding forest cover. A seed sowing experiment showed how trees partly shape plant communities already at the germination stage. Further, responses of functional diversity was mainly driven by resource use related traits among plants and birds, whereas bat functional diversity responses were mainly determined by their ability to manoeuvre through the micro-habitats of wooded pastures. Based on this thesis, I conclude that the tree density limit proposed by the EU has failed to capture the unique biological values of continuously managed wooded pastures and that the social-ecological links between policy, management and biodiversity are threatened by number specific governance of nature. It is therefore promising that the EU in November 2017 announced to open up for excluding the tree density focus in the CAP. Further development of the CAP can benefit from the findings of this thesis, revealing important knowledge gaps on biodiversity patterns in relation to trees in pastures.
|
|
| 4. |
- Roth, Nina, 1984-
(author)
-
Grasslands in a changing climate : Summer drought and winter warming effects on grassland vegetation
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Grasslands harbour a high biodiversity of both plants and animals, and they provide many ecosystem services such as fodder production, pollination, and carbon storage. Climate change is likely to alter grassland ecosystems, with the effects varying according to the exact nature and timing of changes. Hence, understanding of seasonal climate change effects on grasslands and how negative impacts can be reduced is important to maintain biodiversity and to ensure continued delivery of ecosystem services.In this thesis I explored how seasonally specific aspects of climate change, i.e. summer drought and winter warming, affect aboveground plant biomass, plant community composition, and floral resources for pollinating insects. Moreover, I aimed to outline ways to mitigate potential negative climate change effects by adapting conventional grazing and mowing regimes and/or by applying soil amendments (i.e. compost) as a novel management method. Soil amendments have been suggested as a method to increase carbon sequestration and they might mitigate negative drought effects. However, there is no empirical evidence of how European grassland ecosystems would be affected should such measures be applied.A literature review of climate change studies revealed that the terms ‘wetter’ and ‘drier’ can be defined by a variety of hydroclimatic variables, or are not defined at all, making it difficult to synthesise climate change effects on ecosystems and societies. In two in-situ experiments I investigated the effects of summer drought (using rain-out shelters), soil amendments and mowing on four Swedish grasslands, and the effects of winter warming (using open-top chambers) and sheep grazing on three British Upland grasslands. The experimental summer drought caused a non-significant decline in aboveground plant biomass (i.e. fodder production), plant species diversity, and floral resources. Applying soil amendments increased aboveground plant biomass and floral resources (in yearly mown plots), but these positive effects were reduced under drought. There were signs of negative soil amendment effects on legumes. Winter warming led to an increase in graminoid biomass and a decrease in bryophyte biomass. Sheep grazing buffered the growth of a competitive species under winter warming but had only minor effects overall.My thesis emphasizes that it is important to clearly define terms like ‘wetter’ and ‘drier’ when studying effects of climate change on ecosystems, since clarifying the effects of climate across habitats and management interventions will require the synthesis of results across a range of experimental and observational systems. My field experiments indicate that even relatively small climatic changes affect grassland plant biomass and biodiversity, and that these effects depend on the season and grassland site in question. Furthermore, soil amendments have mainly positive effects on the grassland vegetation, indicating that they have potential for broad-scale application as a method to increase carbon sequestration. Given that my experiments were set up in-situ in grasslands and the treatments were rather mild and realistic in magnitude according to local climate change predictions, the observed vegetation changes within only three years are quite remarkable. They therefore highlight the need for detailed empirical and mechanistic understanding of how climate change processes are likely to affect grassland ecosystems.
|
|
| 5. |
- Waldén, Emelie, 1984-
(author)
-
Restoration of semi-natural grasslands : Impacts on biodiversity, ecosystem services and stakeholder perceptions
- 2018
-
Doctoral thesis (other academic/artistic)abstract
- Humans play a major role shaping the living conditions for not only ourselves, but also all other species on Earth. In fact, some species-rich habitat types require human management to uphold the biodiversity and related ecosystem services. One of the world’s most biodiverse habitats on small spatial scales, semi-natural grasslands, have been formed over the course of centuries through extensive grazing and mowing. However, due to political and economic reasons, up to 90% of the European semi-natural grasslands have been lost during the 20th century. To counteract these drastic losses, restoration actions are implemented in environmental policies across Europe. Yet, knowledge of the long-term restoration effects on biodiversity and ecosystem services is still limited. The vast need for future restoration also requires a better understanding of how different pre-conditions affect the restoration outcome, as well as how stakeholders perceive restoration, to be able to prioritise between sites and recognise the limitations of the restoration process. In this thesis, I examine restoration outcomes in Swedish semi-natural grasslands, in terms of plant diversity, associated ecosystem services and from the farmers’ and land-owners’ perspective. The outcome is also analysed in relation to environmental factors at the local and landscape scale. I found that the overall community composition recovered to resemble intact reference communities, but it took relatively long time (12-20 years). Moreover, the reference sites still had higher species richness both at large and small spatial scales, more grassland specialist species and a higher abundance of plant species important to the five tested ecosystem services (meat production, pollination, water retention, temperature regulation and cultural heritage). My results show that prioritising large, unfertilised, newly abandoned grasslands situated in landscapes containing a large grassland specialist species pool and high amounts of intact and remnant semi-natural grasslands, could speed up the plant recovery. However, prioritising fast results does not necessarily ensure long-term success at a larger spatial scale. Since restoration success can be interpreted differently depending on evaluation measure used, pre-defined, clear and realistic goals are essential. While the surveyed farmers and landowners overall perceived the restoration as successful, 40% were unsure whether the grasslands will be managed in the future. Low profitability still poses a threat to their maintenance and thus, also to the coupled biodiversity and ecosystem services. Policy changes are therefore urgently needed to facilitate incentives for sustained management of restored and intact European semi-natural grasslands in a long-term perspective.
|
|
| 6. |
- Helsen, Kenny, et al.
(author)
-
No genetic erosion after five generations for Impatiens glandulifera populationsacross the invaded range in Europe
- 2019
-
In: BMC Genetics. - : BioMed Central. - 1471-2156. ; 20
-
Journal article (peer-reviewed)abstract
- Background: The observation that many alien species become invasive despite low genetic diversity has long been considered the ‘genetic paradox’ in invasion biology. This paradox is often resolved through the temporal buildup genetic diversity through multiple introduction events. These temporal dynamics in genetic diversity are especially important for annual invasive plants that lack a persistent seed bank, for which population persistence is strongly dependent on consecutive seed ‘re-establishment’ in each growing season. Theory predicts that the number of seeds during re-establishment, and the levels of among-population gene flow can strongly affect recolonization dynamics, resulting in either an erosion or build-up of population genetic diversity through time. This study focuses on temporal changes in the population genetic structure of the annual invasive plant Impatiens glandulifera across Europe. We resampled 13 populations in 6 regions along a 1600 km long latitudinal gradient from northern France to central Norway after 5 years, and assessed population genetic diversity with 9 microsatellite markers.Results: Our study suggests sufficiently high numbers of genetically diverse founders during population re- establishment, which prevent the erosion of local genetic diversity. We furthermore observe that I. glanduliferaexperiences significant among-population gene flow, gradually resulting in higher genetic diversity and lower overall genetic differentiation through time. Nonetheless, moderate founder effects concerning population genetic composition (allele frequencies) were evident, especially for smaller populations.Despite the initially low genetic diversity, this species seems to be successful at persisting across its invaded range, and will likely continue to build up higher genetic diversity at the local scale.
|
|
